Process for concentrating all kinds of precious metal ores by froth flotation



Patented Feb. 11, 1936 UNITED STATES PROCESS FOR CONCENTRATING ALL KINDS OF PRECIOUS METAL ORES BY FROTH FLOTATION Carl Gottfried Rudolf Melzer, Langenberg, Germany No Drawing. Application April 17, 1935, Serial Claims.

This invention relates to an improved method of dressing ores for the recovery therefrom of precious metals and/or their minerals such as selenides, tellurides and other compounds by 5 froth flotation.

My invention is based upon the discovery that certain substances are able, under suitable conditions, to become linked with the precious metals and/or their minerals present in the ore pulp to produce linked compounds which can be readily floated.

Suitable substances for my purpose are one or more of the sulphides and/or sulpho salts of lead, copper, mercury and/or silver which I 15 term link forming compounds.

I have discovered that if a link forming compound is produced partly or wholly in colloidal condition it has the property of becoming linked up by adsorption to the precious metal and/or its mineral. However the colloidal and highly dispersed part of the link forming compound is not in itself flotable nor generally is the adsorptively linked combination of the precious metal or mineral therewith except possibly when the individual particles of precious metal or mineral are relatively large.

I have discovered further that the colloidal and highly dispersed link forming compound 30 may be brought into flotable condition by coagulation which is found not to destroy its col loidal nature and consequent'adsorptive linking capacity. The resulting coagulated flakes probably function simultaneously both as'a colloidal 35 material to give the observed high adsorptive capacity and as a coarsely graded material which is flotable.

The process in accordance with my present invention is characterized therefore in that there 40 is caused to be present in the ore pulp a small amount of one or more sulphides and/or sulpho salts of copper, lead, silver, or mercury in coagulated colloidal condition, thereby having the property of becoming linked with the precious 45 metals and/or their minerals to form readily flotable complexes which are then floated by any suitable flotation process. The term sulpho- In Great Britain December 22,

concentration) of a soluble salt of the metal with a dilute alkaline sulphide solution (about 1% concentration), or by passing sulphuretted hydrogen into the metal salt solution. The partially colloidal sulphide so obtained may be 5 treated to coagulate the colloidal portion thereof by heating or better still by slow agitation.

A small proportion of the resulting precipitate will be present in a crystalline condition and the balance in coagulated colloidal condition. The coagulated flakes prepared in this way will therefore always contain enclosed therein a proportion of crystalline particles which in themselves are not essential to the carrying out of my process since they have no definite absorptive capacity. The active reagent is added to the pulp either before or during flotation or after a period of preliminary flotation.

A satisfactory link forming reagent may also be obtained by disintegrating the corresponding naturally occurring minerals such as galenite or argentite to a very finely divided state and subsequently coagulating the colloidal portion.

I am aware that in an already known process for the recovery of gold from pyritic ores, such as the ores of the Rand, wherein the pyrites and the gold are floated together in a neutral or slightly alkaline pulp using frothing agents containing phenol and/or cresol, it has been proposed, either before flotation or after an initial flotation, to precipitate metallic sulphide, such as ferrous sulphide, chemically in the pulp, and to follow this by a subsequent flotation to give an improved or further proportion of pyrites and gold in the froth. This proposal is distinguished from my present process in that there was no suggestion of using the metallic sulphide in coagulated colloidal condition. Furthermore in the already proposed process the use of ferrous o sulphide is recommended. Now this compound does not to my knowledge become directly linked to any extent either with the precious metals and/or their minerals or with the pyrites, and is consequently of no use for my purpose.

The subsequent process of actual flotation forms no essential feature of my invention. Where-lead sulphide has been used as the link forming compound, flotation should be carried out in a slightly alkaline pulp; a xanthate may conveniently be used as collector and aerofloat (a product of the American Cyanamid Co.) or cresol as frothing agent. The pulp is brought to froth flotation in a suitable apparatus wherein the linked compound between the precious 86 metal and the active lead sulphide separates out quantitatively after a short period. The flotation is finished when a further separation of lead sulphide in the froth can no longer be observed.

It is evident that for the purposes of linking the precious metals and/or their minerals only very small proportions of the above-mentioned sulphides or sulpho salts suiflce, for instance 300 grams per ton of ore.

The following are examples of the manner in which my invention can be carried into practice:--

Example 1 The treatment of a Transylvanian are containing about 5% of pyrites and a small proportion of chalcopyrite, the majority of the gold being free but a small proportion thereof being in the form of crystals grown together with pyrites, is a good example of the advantages obtained by my method of directly linking up the gold with the active sulphide and separating it in this form as opposed to the known methods wherein the gold can only be separated together with the pyrites in the form of a poor concentrate.

My process was applied to this ore in such a manner as to link up the free proportion of the gold with lead sulphide by addition of active 7 25 com. of the 1% lead acetate solution were used; 1 com. of a 1% solution of reagent 301" (American Cyanamid Company); 3 com. of a 1% solution of aerofloat 15" (American Cyanamid Company).

The concentrate obtained was once cleaned and yielded 2.93 gr. of concentrate and 2.58 gr. of middlings which in practice would be reintroduced into the first flotation-cycle. The tailings of this first flotation were floated again with the addition of 1 com. of a 15% CuSO4-solution (for reactivation of the pyrites) 8 ccm. of a. 1% solution of reagent 301" 3 com. of a 1% solution of aerofloat 15 15.2 gr. of pyrite concentrate were obtained,

which were not cleaned.

Subsequently active PbS prepared as described above from 25 com. of a 1% lead acetate solution was added. The concentrate obtained was cleaned once and yielded 1.59 gr. of concentrate and 3.83 gr. of middlings. The proportion of tailings amounted to 211 gr.

lead sulphide. At the same time the pyrites were An analysis of the separate products gives the depressed in known manner. With the first flofollowing figures:-

Granirgies per Extraction Products Grammes Mflhgiagmmes Milligglmmes Ag Au Percent Ag Percent Au Concentrate 1 2. 93 2, 454 378. 8 7. 19 1. 62. 0 77. 5 Middlings of 1 2. 58 40 34. 9 0. 10 0. 090 0. 9 6. 3

Total- 62. 9 83. 8 Concentrate 2 yrites concentrate) 15. 20 10. 0 97 0. 152 17. 0 10. 6 Concentrate 3 (PbS-con centrate) 1. 59 189 18. 9 0.30 0. 030 2. 6 2. 1

Tot 82.5 96. 5 Middlings of 3 3. Tr. Tr. Tr. Tr. Tailings 211. 00 10 0. 24 2. 04 0. 051 17. 5 3. 5

Ore contained 237. 00 49 6. 0 11- 60 1. 433 100. 00 100. 00

tation a rich PbS-concentrate which already Example 2 contained 83.8% of the total proportion of the gold was obtained. With the second flotation the pyrites were made flotable againby known methods(reactivated) and a pyrite concentrate very poor in gold was obtained. Subsequently active lead sulphide was again added in order to link up with the last remnants of the precious metal and in this way a third lead sulphide concentrate poor in. gold was obtained. In practice this third concentrate should be re-used as a reagent in the first flotation (where the pyrites are depressed) so that as a result only a lead sulphide concentrate rich in gold and a pyrite concentrate poor in gold are obtair ed.

The experiment was carried out as follows: Test-portion of ore:

250 gr. disintegrated together with 200 mgr. of sodium carbonate 14 mgr. of sodium cyanide 4 com. of water glass solution 500 com. of water I Fineness of the disintegrated mass:

5.5% plus 200 meshes (per linear inch). After dilution with water in the flotation cell to 1.25 litres the ore was floated with the addition of active lead sulphide, prepared by precipitation of a 1% lead acetate solution by a 1% sodium sulphide solution and coagulation of the finely divided sulphide so generated by agitation.

An example of an ore of Sumatra not containing any pyrites and substantially only free gold is the following: The ore was disintegrated to a fineness of minus 10 meshes per linear inch,

the test portion of 250 gr. of ore being ground to- 7 in the same way as in the first example from 25 com. of 1% solution of lead acetate. The concentrate obtained was cleaned once. An analysis of the separate products gives the following flgures:

Gramrnes Percent Product Grammes per ton Au gragilrlnes 01A PbS-concentrate-.. 0. 410 6, 463. 4 2. 650 93. 9 Middlings 6.1 8.2 0.050 1.8 Tailings 241.00 0.5 0.121 r 4.3

Ore contained- 247. 5 11. 4 2. 821 100.0

This experiment shows quite clearly that the gold is definitely linked up with the lead sulphide added. Further, this example demonstrates that the presence of coarse pyrites is not necessary to the successful carrying out of the invention.

I claim as my invention:--

1. In the process of treating precious metal containing ores which comprises subjecting the ore pulp to the action of a reagent selected from the group consisting of the sulphides and sulpho salts of copper, lead, silver, mercury, said reagent being present in a coagulated colloidal condition, and subjecting the mass to froth flotation.

2. The process according to claim 1 wherein the coagulated colloidal reagent is in admixture with a portion of the reagent in the form of crystalline particles.

3. In the process of treating precious metal containing ores which comprises subjecting the ore pulp to the action of a reagent selected from the group consisting of a sulphide of copper, lead, silver, mercury, said reagent being present in a coagulated colloidal condition, and subject ing the mass to froth flotation.

4. The process according to claim 1 in which the reagent is that obtained by disintegrating naturally occurring sulfides and treating the disintegrated sulfides to coagulate the colloidal portion thereof.

5. The process of recovering precious metals from ores containing them which comprises subjecting the ore pulp to the action of a reagent selected from the group consisting of the sulphides and sulpho salts of copper, lead, silver, mercury, said reagent being present in a coagulated colloidal condition, subjecting the mass to froth flotation, and reusing the concentrate from the froth flotation as a reagent for treating further ore pulp.

CARL GO'II'FRIED RUDOLF MELZER. 

